This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. Primary support for the subproject and the subproject's principal investigator may have been provided by other sources, including other NIH sources. The Total Cost listed for the subproject likely represents the estimated amount of Center infrastructure utilized by the subproject, not direct funding provided by the NCRR grant to the subproject or subproject staff. Recent developments in applied mathematics have yielded an analytic Green's function to the Boltmann Transport Equation (BTE) which provides an exact description for photon migration in turbid media. The use of a Green's function rather than Monte Carlo simulations promises to model important problems with much less computational expense. We are investigating approaches to utilizing this solutions to address important forward and inverse problems of photon migration in homogeneous and heterogeneous tissues using this approach. We are also working on incorporating the Green's function based ERT kernel into the Solver module of the Virtual Tissue Simulator.